Wednesday's 2-1 defeat by Germany, following the opening loss to Denmark, leaves one of the pre-tournament favourites and World Cup finalists two years ago without a point at the foot of Group B.
"We know that our game needs to improve. We need to get our routines on the pitch back, the things we are used to, the courage to play," Sneijder told reporters.
"Maybe in that last game, because we know we have to win it, there'll be no other chance. It's all or nothing on Sunday and perhaps we can bring our own football back in that game."
Even then goal difference in the games between the teams on three points would come into play but none of that will matter if Bert van Marwijk's side are unable to solve the numerous problems afflicting them.
"There is no cohesion between our lines, there are gaps and we are not connecting and then it is very difficult to recover the ball," he remarked.
"At the moment we are not steady as a team like we were two years ago and there is not one area to blame. We failed as a team.
"Now we have to hope that Germany will do their duty against the Danes and we have to avenge our first two defeats and hope.
"We are not in control now and that doesn't feel good."
While Robin van Persie's superbly taken second-half goal against Germany will boost his confidence and Robben is always capable of something special, a greater concern will be the way Germany carved open the Dutch defence in the first half with two strikes from Mario Gomez.
"One thing we did know was that Holland are not so good in one-on-ones in defence and that's how the two goals came about," he said.
"There were little spaces next to Mathijsen and Heitinga and we knew if we could get in there it would be very dangerous for Holland."
"The last two years, we as technical staff spent a lot of time to see if there are fresh names for this team but they have to be available," he said.
"Now we have to work out a plan to beat Portugal with a two goal deficit [in the group]."
